Plus, why would OP serve the customer after the bill? Don't you pay the bill when you're done being served? Unless if you want to deliberately go out of your way to spill coffee, which would make the person who was supposed to get the coffee angry as well. There's no good that would come out of that.

#32: It depends on how nice you are to your waiter and how well you tip them. Usually, when I go to a new restaurant, even after I've paid my bill and leave tip, my waiter will still come back and refill my drink. I imagine they wouldn't do that if they weren't satisfied with the tip I left. Just leave 12% as a rule of thumb (unless the service was genuinely bad, and it has happened before), and they'll be grateful for that.

12%? That's harsh. Most servers have to tip out a percentage of their sales, myself a minimum of 4%. Better rule of thumb: 18-20% for good service, 15% for mediocre service, 10% if it's bad. Stiffing is only reserved for the rudest, shittiest of service.